POTENTIOMETRIC DISCRIMINATION BETWEEN PLANAR AND OCTAHEDRAL ANIONIC METAL CYANO COMPLEXES BY LIQUID MEMBRANE ELECTRODES BASED ON LIPOPHILICMACROCYCLIC DIOXOPOLYAMINES

A novel type of poly(vinyl chloride) matrix liquid membrane electrodes that are capable of discriminating between planar and octahedral anio nic metal cyano complexes has been developed by exploiting as the sens ory elements lipophilic derivatives of macrocyclic dioxopolyamines cyl -1,4,8,11-tetraaza-12,14-dioxocyclotetradecane, -1,4,7,10,13-pentaaza- 14,16-dioxocyclohexadecane). Potentiometric response behaviors of thes e electrodes for a series of anionic metal cyano complexes were compar ed with those of the electrodes based on the corresponding nondioxo ma crocyclic pentaamine (15-hexadecyl-1,4,7,10,13-pentaazacyclohexadecane ) as well as a conventional anion exchanger (Capriquat(R)). The electr odes based on the dioxopolyamines displayed strong potentiometric resp onses at pH 4.0 to the metal cyano complexes having a planar structure ([Ni(CN)4]2-, [Pt(CN)4]2-). In contrast, the responses to the metal c yano complexes having an octahedral structure ([Fe(CN)6]3-, [Fe(CN)6]4 -) were only negligible. On the other hand, for all of the guests test ed, the electrodes based on the nondioxo macrocyclic pentaamine or the anion exchanger showed strong linear responses to both planar and oct ahedral complexes. These results represent a new mode of potentiometri c discrimination displayed by dioxo-type macrocyclic polyamines having both amine and amide moieties.